play group ettiqute

Ok, this is dumb but I have no where else to ask it. We were invited to a playdate this Friday to a twin mom's house that I recently met. And she didn't realize that her playgroup was meeting at her house the same morning but she invited us to join them rather than cancel since my twins are in the same age group and all. We have never been to a playgroup playdate so I am just wondering what the appropriate etiquette is and if it would even apply to me since I am not an official part of the group. We will only be staying maybe 2 hours, but I am wondering if I bring something for the host or some sort of snack for her to serve or even a little something for each of the children(or at least the hostess' children). I feel funny going empty handed. I would have posted this on my twin board but a mutual friend of ours posts there too and I guess I would feel dumb if she saw this or even worse said something to our friend the hostess. So hopefully people will see this and maybe even responds in time for the playdate. I never post here, so I am not sure how many people check this but I figured it was worth a shot.